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Sufficient Pressure (sufficient + pressure)

Distribution by Scientific Domains

Medical Sciences	50%

Selected Abstracts

Eutectic Gallium-Indium (EGaIn): A Liquid Metal Alloy for the Formation of Stable Structures in Microchannels at Room Temperature,

ADVANCED FUNCTIONAL MATERIALS, Issue 7 2008
Michael D. Dickey
Abstract This paper describes the rheological behavior of the liquid metal eutectic gallium-indium (EGaIn) as it is injected into microfluidic channels to form stable microstructures of liquid metal. EGaIn is well- ;suited for this application because of its rheological properties at room temperature: it behaves like an elastic material until it experiences a critical surface stress, at which point it yields and flows readily. These properties allow EGaIn to fill microchannels rapidly when sufficient pressure is applied to the inlet of the channels, yet maintain structural stability within the channels once ambient pressure is restored. Experiments conducted in microfluidic channels, and in a parallel-plate rheometer, suggest that EGaIn's behavior is dictated by the properties of its surface (predominantly gallium oxide, as determined by Auger measurement s); these two experiments both yield approximately the same number for the critical surface stress required to induce EGaIn to flow (,0 .5,N/m). This analysis,which shows that the pressure that must be exceeded for EGaIn to flow through a microchannel is inversely proportional to the critical (i.e., smallest) dimension of the channel,is useful to guide future fabrication of microfluidic channels to mold EGaIn into functional microstructures. [source]

Reverse flow facial artery as recipient vessel for perforator flaps

MICROSURGERY, Issue 6 2009
D.D.S., Frank Hölzle M.D., Ph.D.
In perforator flaps, anastomosis between flap and recipient vessels in the neck area is often difficult due to small vessel diameter and short pedicle. The aim of this study was to investigate whether the retrograde flow of the distal, paramandibular part of the facial artery would provide sufficient pressure and size to perfuse perforator flaps. Before and after occlusion of the contralateral facial artery, retrograde and anterograde arterial pressure was measured on both sides of the facial artery in 50 patients. The values were compared with the mean systemic arterial pressure. Diameters of facial arteries in the paramandibular region and perforator flap vessels were evaluated by morphometry. Arterial pressure in the distal facial artery with retrograde flow was 76% of the systemic arterial pressure. The latter equaled approximately the anterograde arterial pressure in the proximal end of the facial artery. Mean arterial pressure of the facial arteries decreased after proximal occlusion of the contralateral facial artery, which was not significant (P = 0.09). Mean diameter of the distal facial arteries in the mandibular region was 1.6 mm (range 1.3,2.2 mm; standard deviation 0.3 mm; n = 50), that of the perforator flap arteries 1.3 mm (0.9,2.6 mm; 0.4 mm; n = 20). Facial arteries, based on reverse flow, successfully supported all 20 perforator flaps. Retrograde pulsatile flow in the distal facial artery sustains perforator flaps even if the contralateral facial artery is occluded. Proximity of the distal facial arteries to the defect compensates for short pedicles. Matching diameters of the arteries are ideal for end-to-end anastomosis. © 2009 Wiley-Liss, Inc. Microsurgery, 2009. [source]

The pressure required to force liquid through breathing system filters,

ANAESTHESIA, Issue 5 2006
C. Cann
Summary Liquid in the form of sputum and condensation may be forced through a breathing system filter if sufficient pressure is applied to the filter layer, with the potential for cross-infection. Twenty-three different breathing system filters (12 adult, 11 paediatric) were assessed to determine the pressure causing liquid penetration. Five samples of each were tested by connecting the ventilator end of a breathing system filter to a water-filled U-tube and reservoir. The reservoir was positioned so that the water surface was level with the filter layer and raised until liquid appeared through the filter layer on the patient side and the water-column height recorded. There were substantial differences in performance between models. Liquid penetration occurred at lower pressures for adult electrostatic than adult pleated filters: median [IQR] 1.18 [1.08, 1.32] and 8.04 [4.27,12.80] kPa, respectively, p < 0.0001. Liquid penetration occurred at similar pressures in paediatric electrostatic filters (0.98 [0.74,1.32] kPa) compared to adult electrostatic filters. [source]

Dispersal pattern of domestic cats (Felis catus) in a promiscuous urban population: do females disperse or die?

JOURNAL OF ANIMAL ECOLOGY, Issue 2 2003
Sébastien Devillard
Summary 1The domestic feral cat (Felis catus L.) is a good model for studying intraspecific variability of dispersal patterns in mammals because cats live under a large diversity of socio-ecological conditions. We analysed both the natal and breeding dispersal patterns of domestic cats in a promiscuous urban population and tested whether or not it differed from the male-biased natal dispersal pattern observed for polygynous rural populations. 2During an 8-year study we recorded the exact date of in situ death for 148 marked cats and the exact date of disappearance from the population for 99 other cats. Because undiscovered deaths might over-estimate dispersal probabilities when considering only disappearance probabilities, we made an novel application of multistrata capture,recapture methods in order to disentangle dispersal from true mortality. 3We showed that mature females dispersed, both before and after their first reproduction, at 1 and 2 years old. Contrary to females, no dispersal seemed to occur in males. Before sexual maturity, females that disappeared at 1 and 2 years old were in worse body condition than females that stayed in the population area after 2 years old. However, they did not reproduce less successfully before their disappearance than females that died later in the population area. 4The female-biased and low natal dispersal pattern in this population was atypical compared to other promiscuous/polygynous mammals and differed from that observed in rural polygynous populations of domestic cat. Neither local mate competition nor inbreeding avoidance appeared to be sufficient pressures to counterbalance ecological constraints on dispersal in an urban environment. However, local resource competition for den sites between potential matriarchies could lead to the breeding dispersal of less competitive females. [source]